[University Research] Bed Bug ‘Bug Bombs’ Busted!

Features - Special Report

Research out of Ohio State finds foggers have little impact on modern-day bed bugs due to the brief exposure times, their relatively low concentrations of pyrethrins and/or pyrethroids, and their lack of residual activity. And, the insecticide mist from such foggers had no adverse effects on any bed bugs that were in harborages — their typical location.

For decades, “bug bombs” or “foggers” have been sold as over-the-counter (OTC) products for consumer use against many common household insects. Foggers act by broadcasting an insecticide mist by way of an aerosol propellant. These products typically are easy to use and require little effort, and they are commonly used by consumers as a low-cost alternative or supplement to professional pest control services. The U.S. Environmental Protection Agency (EPA) recently estimated that about 50 million foggers are used annually in the United States (http://1.usa.gov/S0pMMM).

The name “bug bomb” seems rather fitting given that explosions have been reported when excessive numbers of foggers have been used or when a nearby ignition source, such as a pilot light, has remained on during fogging. Such explosions are newsmakers worldwide.

Furthermore, foggers have been implicated in human injury and illnesses, often due to misuse of the products by consumers. The U.S. Centers for Disease Control and Prevention (CDC) reported 466 cases of acute, pesticide-related illness or injury associated with exposure to total-release foggers in eight states between 2001 and 2006 (Wheeler et al. 2008). In an effort to minimize misuse of foggers, EPA required manufacturers to make a number of labeling changes by Sept. 30, 2011, to enhance clarity and to draw increased attention to critical information (http://1.usa.gov/S0pMMM).

So…are these products effective against household insects? Many members of the pest management industry have expressed concern that foggers appear to be largely ineffective, particularly against crawling insects that are not on exposed surfaces. Furthermore, there is the general perception in the industry that foggers can actually make matters worse by causing insects to scatter from the treated area into untreated or adjacent areas.

Indeed, a study by Ballard et al. (1984) showed that German cockroaches moved from fogged units to adjacent units in 50 percent of apartments, with increased catches of cockroaches the night following the fogger treatment. Furthermore, German cockroaches prematurely released their oothecae (egg cases), resulting in an increase in newly hatched nymphs in response to fogging with pyrethrins (Kardatzke et al. 1982) or dichlorvos (Ballard et al. 1984). Hence, fogging actually has been shown to increase problems with some insects.

Bed bugs have made a worldwide comeback, and the market now is inundated with consumer products for bed bug control. Some of the product claims are rather incredible, and one could easily imagine that such products should solve our bed bug problems. But instead, bed bugs are an increasingly worrisome urban pest in communities nationwide.

Not unexpectedly, foggers are a common OTC product used against bed bugs. However, prior to our current study, there was no published information regarding the efficacy of foggers against bed bugs. Pyrethrins and pyrethroids (synthetic versions of pyrethrins) are the most common active ingredients in OTC foggers, but there is concern regarding their effectiveness given that pyrethroid resistance is well documented and widespread in field-collected bed bugs and has been implicated in the resurgence and challenge of bed bug control (Romero et al. 2007, Zhu et al. 2010, Bai et al. 2011).

In our study, we tested three different fogger brands obtained from a nationwide retailer to assess their effectiveness against bed bugs. One of these products, the Hotshot Bedbug and Flea Fogger (0.05% pyrethrins, 0.1% esfenvalerate, 0.1% piperonyl butoxide, 0.167% MGK 264, 0.1% nylar), is specifically labeled for use against bed bugs and claims it “kills on contact” and provides “effective long-term control.” Our most extensive testing was done with the Hotshot Fogger because it specifically is marketed for use against bed bugs (and fleas).

We also tested Spectracide Bug Stop Indoor Fogger (0.1% tetramethrin, 0.6% cypermethrin) and Eliminator Indoor Fogger (0.515% cypermethrin), which are labeled for use against flying and crawling pests in homes. Neither of these two products lists bed bugs on its label. Nonetheless, these foggers can be used against bed bugs in many states, whose regulatory requirements are that only the site (e.g., indoors) has to be specified by the label, not the particular pest.

Materials and Methods. A variety of bed bug strains and exposure techniques were used.

Study Site. Experiments were conducted in three rooms in a vacant office building on Ohio State University’s Columbus campus. The volume of the two treatment rooms was 1,190 cubic feet and 1,280 cubic feet, and the control room was 1,330 cubic feet — all considerably less than 2,000 cubic feet, which is the maximum space prescribed for the tested foggers. Prior to evaluating the foggers, we installed 6 millimeter plastic sheeting to cover drop ceilings, outlets and vents in each room to prevent dispersion of the insecticide into adjacent areas.

Bed Bugs. We tested field populations of bed bugs (EPM, King, Kingry, Marcia and Pointe), all of which were collected between July 2010 and March 2011 from residences in Columbus, Ohio, and subsequently reared in our Ohio State University laboratory.

Additionally, we tested the Harlan strain, which has been laboratory-raised since 1973 without insecticide exposure. The Harlan strain is a known pyrethroid-susceptible population that served as an internal control in our experiments. An internal control is used to confirm acceptability of the product testing protocol because expected adverse effects can be seen in susceptible insects. Additionally, since the Harlan strain is widely used as a standard susceptible population in bed bug research, it allows for comparison of data among research labs.

In the lab, each bed bug population was housed in a glass narrow-mouth Mason pint jar. Bugs were fed chicken blood using a Hemotek artificial feeding system.

Exposure Conditions. Test arenas consisted of petri dishes or cylindrical plastic containers whose sides had been coated with a slippery material, Fluon, to prevent bed bug escape. A group of nymphs or adults was placed inside each arena, with each replicate consisting of five nymphs or five adults, except in forced harborage experiments where groups of 10 were used.

Direct Exposure Experiments. Bed bugs were placed inside empty, open arenas. They were directly exposed to the insecticide mist from the fogger, and they had no way to avoid exposure.
In direct exposure experiments, the Hotshot Fogger was evaluated against a total of 600 bed bugs from the five field populations and the Harlan strain. The Spectracide Fogger and Eliminator Fogger were each evaluated against a total of 300 bed bugs from two field populations and the Harlan strain.

Optional Harborage Experiments. Bed bugs were placed inside open arenas, each of which contained a filter paper disc. The bugs had the option of remaining out in the open or moving to the underside of the disc where the insecticide mist could not reach, due to the mist being unable to penetrate through paper.
In optional harborage experiments, the Hotshot Fogger was evaluated against a total of 600 bed bugs from the five field populations and the Harlan strain. The Spectracide Fogger was evaluated against a total of 300 bed bugs from two field populations and the Harlan strain. Optional harborage experiments with the Eliminator Fogger were thwarted when the insecticide mist caused the filter paper harborages to curl, allowing some bugs to escape from their arenas into the wading pools (where they were confined because of the Fluon coating on the pool walls).

Forced Harborage Experiments. Bed bugs were placed inside empty arenas, each of which was then covered with a single layer of light-weight cotton fabric that was held in place by a rubber band. These bugs had no place to hide inside an arena, thus would be contacted by any insecticide that penetrated through the thin fabric covering.
Only the Hotshot Fogger was evaluated in forced harborage experiments, and a single field population and the Harlan strain were tested using two exposure conditions — presence or absence of a fabric covering, the latter situation essentially representing direct exposure conditions. A total of 800 bed bugs were used in this set of bioassays.

Experimental Conditions. At the study site, two wading pools (44-inch diameter) with Fluon-coated inner walls were situated in each room so that two exposure conditions could be simultaneously evaluated for each fogger. Replicates then were positioned inside each wading pool so that the various populations and/or stages were randomly distributed. The fogger can was positioned on a crate between the two pools such that it was about 1 foot above the floor and about 1 foot from each pool edge (see photos above). As specified by the directions, the fogger was activated for two hours in a closed room, then the room was ventilated for 30 minutes. A control room was similarly configured but without the fogger.

The condition of bed bugs was assessed upon re-entry (30 minutes), again at 24 hours and again at five to seven days. Bed bugs were examined using a dissecting microscope as necessary. Each bug’s condition was assessed based on its behavioral response when probed — healthy bugs are those that move quickly and in a coordinated manner to avoid stimulus (probing). Toward the opposite end of the behavioral spectrum, moribund bugs cannot walk, but their appendages or other body parts show signs of movement. Dead bugs have no signs of movement whatsoever.

Results. Results for each fogger differed slightly based on which strain of bed bugs was used. Field-collected bed bugs showed few adverse effects.

Hotshot Fogger.Direct Exposure Experiments. All five field-collected bed bug populations showed negligible adverse effects after two hours of direct exposure to the aerosolized pyrethrins and pyrethroid from the Hotshot Fogger (see Figure 1 below). The vast majority of nymph and adult bed bugs from these field populations remained healthy at all observations (re-entry, 24 hours and five to seven days) despite having been directly contacted by the aerosolized insecticide during the two-hour fogger treatment. Overall, in treatment and control groups, bed bug mortality averaged 2.1 percent and was non-significant. A minor exception was Pointe bugs, with 28 percent mortality observed five to seven days after exposure to the fogger. Also, 24 percent mortality was observed at five to seven days for Harlan control bugs.

Only the susceptible Harlan strain experienced significantly high mortality, and 100 percent of the Harlan bugs were moribund or dead at re-entry after having been directly contacted by the aerosolized insecticide from the Hotshot Fogger (see Figure 1, without harborage). As an internal control, the expected response of the Harlan bed bugs indicated that the fogger was functioning properly and the aerosolized insecticide was reaching all arenas in the room.

Optional Harborage Experiments. As in the direct exposure experiments, all five field-collected bed bug populations showed negligible adverse effects after two hours of exposure to the Hotshot Fogger (see Figure 1, with optional harborage). Further-more, when the susceptible Harlan population was provided an optional harborage, mortality at re-entry (62 percent) was significantly lower than in the direct exposure experiments, but mortality progressed over time (78 percent mortality at 24 hours, and 100 percent at five to seven days) (see Figure 1, with optional harborage). Hence, some of the Harlan bugs apparently took cover underneath the filter paper, but not before receiving a toxic dose of the insecticide.

Forced Harborage Experiments. Results from this set of experiments (see Figure 2 below) are particularly important because susceptible Harlan bed bugs were observed to be unaffected by the Hotshot Fogger if nymphs and adults were covered by a thin cloth layer that provided harborage. The field-collected EPM population was unaffected by the Hotshot Fogger regardless of whether bugs were directly exposed or inside a harborage. Note that data are shown only for re-entry and 24-hour observations because of somewhat high control mortality (16.5 percent) at five to seven days.

Spectracide Fogger.Direct Exposure and Optional Harborage Experiments. When exposed to the Spectracide Fogger, the mortality trend among populations was Harlan greater than EPM, EPM greater than Marcia. Harlan bed bugs experienced significantly higher mortality in open dishes (100 percent) than when they had access to a harborage (69 percent); mean mortality of Harlan bugs further increased to 91 percent at 24 hours and to 98 percent at five to seven days (see Figure 3 below). Additionally, EPM bugs in open dishes had a significant increase in mortality from 0 percent (re-entry) to 24 percent (24 hours) to 66 percent (five to seven days). However, when EPM bugs had access to a harborage, their mortality was very low, equivalent to controls. Marcia bed bugs exhibited very low mortality (equivalent to controls) at re-entry, 24 hours, and five to seven days regardless of harborage.

Eliminator Fogger.Direct Exposure Experiments. There were no significant adverse effects for bed bugs from two field-collected populations, EPM and Marcia, at re-entry and 24 hours after being directly exposed in open containers to the Eliminator Fogger (see Figure 4 below). Because control mortality was excessive (37.8 percent) at the five to seven days observation, data from this observation time were omitted. Otherwise, overall mortality was quite low for controls (6 percent) as well as for Marcia (8 percent) and EPM (3 percent) exposed to the fogger. Significantly high mortality was observed only for the susceptible Harlan strain.

Discussion. Field-collected bed bugs typically were not affected by direct exposure for two hours to the aerosolized pyrethroid(s) emanating from any of the three total-release foggers, with a few minor exceptions. In contrast, the Harlan strain, the long-term laboratory population that is susceptible to pyrethroids, experienced significantly high mortality when directly exposed to any of the three foggers. Hence, pyrethroid resistance appeared to play a role in the foggers’ failure to kill bed bugs.

At the conclusion of this study, individuals from the five field populations were genotyped, and all had both known knockdown resistance (kdr) mutations involved in pyrethroid resistance [see Zhu et al. (2010) for more information on these kdr mutations]. When exposed to dried residues of deltamethrin (a pyrethroid), all field populations were resistant.

A very important finding from this study was that a forced harborage negated any fogger effects on the susceptible Harlan strain. Furthermore, having access to an optional paper harborage resulted in delayed mortality in susceptible Harlan bugs and significantly reduced mortality for EPM bugs exposed to Spectracide. Hence, our research supports the view that total-release foggers lack the ability to penetrate into typical harborages utilized by many household insects, therefore rendering these products ineffective as control agents. Our findings provide support for Osbrink’s et al. (1986) suggestion that reduced mortality of cat fleas on disks of carpet vs. filter paper was likely due to the carpet providing a refuge for cat fleas to avoid the mist from foggers.

In residences and other settings, the majority of bed bugs (more than 80 percent) hide in protected sites during the day regardless of their feeding status (Reis and Miller 2011). Furthermore, fed bed bugs do not leave their harborages to search for a blood meal. The innate behavior of bed bugs to remain in tight, inaccessible harborages for a prolonged period of time has important implications for fogger efficacy against bed bug populations. Because of bed bugs’ propensity to remain inside harborages, the majority of the infestation will not occur on open surfaces that allow for direct contact by the insecticide mist from total-release foggers, hence rendering these products ineffective as control agents.

The potential of foggers to scatter bed bugs needs to be evaluated as it may increase the difficulties associated with bed bug control. Bed bugs are notoriously difficult to control in multi-unit buildings (Wang et al. 2009, Harlan et al. 2008, Eddy and Jones 2011), and any product that further disperses the bed bugs to adjacent units is of serious concern.

The EPA Pesticide Regulation Section was notified months ago of our study results, yet there is no indication of whether EPA intends to review the manufacturer’s efficacy data for bed bugs. The public is ill-served when products do not perform in accordance with their claims. When people use ineffective insecticide products, they are not only wasting money, but they are delaying effective treatment of pests whose populations are ever increasing in their residence and likely spreading to others. Furthermore, insecticides are unnecessarily being introduced into the environment, and insects are being exposed to insecticide residues that further reinforce insecticide resistance. The concerned public should speak out.

Our study provides strong evidence that Hotshot Bedbug and Flea Fogger, Spectracide Bug Stop Indoor Fogger, and Eliminator Indoor Fogger were ineffective as bed bug control agents. These foggers had little impact on modern-day bed bugs due to brief exposure times, their relatively low concentrations of pyrethrins and/or pyrethroids, and their lack of residual activity. Most significantly, the insecticide mist from such foggers had no adverse effects on pyrethroid-susceptible and resistant bed bugs that were in harborages — their typical location. Our data also support the position that currently marketed OTC total-release foggers should not be recommended for treating bed bug infestations since the insecticide mist does not penetrate into typical bed bug harborage sites.

The authors are associate professor and research associate in the Department of Entomology, The Ohio State University.

Authors’ Acknowledgments: We thank Andrew Hoelmer, Mark Janowiecki and Thomas Peterson for their assistance with this study. We also acknowledge Harold Harlan’s contribution of susceptible bed bugs. This research was supported in part by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University.